Technical Field
This disclosure relates generally to valves for shutting off flow in a pressurized pipe or conduit. More specifically, this disclosure relates to valves that are installable in a pressurized pipe without shutting off flow to the pipe during installation. Still more specifically, this disclosure relates to improvements in the designs of gate valves, which increase the pressure rating of the valves.
Description of the Related Art
Pressurized conduits or pipes convey fluids, both liquid and gas, in municipalities, industrial plants and commercial installations. When originally installed, a network of pipes may include block valves used to isolate certain sections of the pipe for repairs, relocation or installation of new components into the pipe. When a shutdown is required in a municipal water system, a large area may be deprived of water service. Accordingly, in addition to the inconvenience to residents, schools, hospitals, commercial and/or industrial facilities may have to be shut down until water service is restored.
The length of pipe that needs to be isolated can be shortened and fewer people inconvenienced by adding additional valves, in conjunction with the preexisting block valves. The additional valves may be of the form that can be installed in a pressurized pipe without service interruption and with minimal fluid loss. If such a valve is installed, upon closure of the added valve and completion of the work on the depressurized damaged section of the pipe, the additional valve may be opened or retracted and the block valves are opened, thereby restoring flow through the repaired section of pipe. The additional valves are known in the art under a variety of names, such as inserting valves, add-on valves, insertable gate valves, etc. Examples can be found in the commonly assigned U.S. Pat. Nos. 6,810,903 and 8,627,843.
Typically, such valves include a housing clamped to and communicating with the pressurized conduit that is known in the art as a nozzle or a nozzle assembly. In most cases, the nozzle includes a cylindrical housing section that is clamped perpendicular and pressure-tight to the outside of the pipe by a saddle assembly as shown in FIG. 27 of the '903 patent. Communication between the nozzle and pipe is established by a process called pressure tapping, hot tapping or under-pressure tapping. This process is well known in prior art, and utilizes a temporary valve, such as a knife valve, to allow a cutting device and a new valve to be mounted to the pipe without significant loss of fluid pressure or fluid flow. Specifically, after the pipe is cut, the additional valve can be passed through the temporary knife valve into the nozzle, where it may be held until the pipe needs to be closed. To stop flow, the valve body is moved from the nozzle into the pipe.
Some valves added to municipal pipe systems are intended for temporary service, often in emergencies, while other valves are designed for permanent installation into a pressurized pipe. Each permanent valve is provided with an internal jackscrew-type actuator that allows the valve to be operated as a conventional block valve that is opened and closed by a worker by merely turning a handle or a wrench. This type of permanent valve can be used in emergencies in the same manner as a temporary valve and then abandoned.
The current method of manufacturing of these valves is very labor intensive and has large amounts of machining and welding. Referring to FIG. 1 of the '903 patent, before use, the upper end of the nozzle 46 must be welded to the flange that connects the nozzle 46 to the temporary knife valve 38. Further, the lower end of the nozzle 46 must be welded to the upper saddle member 52 after an opening is plasma cut in the upper saddle member 52. Welding the lower end of the nozzle 46 to the upper saddle member 52 is difficult as the welding material is prone to seeping between the lower end of the nozzle 46 and the upper saddle member 52. Further, pipes having a common internal diameter (ID), e.g., eight inches, may have varying outer diameters (ODs), depending on the thickness of the pipe 32, the material used to fabricate the pipe 32, the pressure rating of the pipe 32 and the end use. To control costs, the size of the nozzle 46 is varied for each pipe ID, not each pipe OD, while the size of the upper and lower saddle members 52, 50 must varied for each pipe OD to ensure a pressure tight connection between the upper saddle member 52 and the pipe 32. As a result, the lower end of the nozzle 46 may not have a diameter that matches that of the upper saddle member 52, which exacerbates the problem of welding material seeping between the lower end of the nozzle 46 and the upper saddle member 52.
Other problems associated with the valve assemblies illustrated in the '903 and '843 patents include difficulties associated with installing the valves below ground level because the nozzles 46 are not equipped with a structure that can be used to tether the nozzle 46 to a winch. Further, currently employed gate valves, like the one shown at 44 in FIG. 1 of the '903 patent, typically include a paddle or gate 180 coupled to a housing structure known as a bullet or a cartridge that protects the paddle 180 as the cartridge and the paddle 180 are lowered through the nozzle 46 and into the pipe 32. The cartridge needs to be equipped with an upper circumferential seal (not shown) that prevents fluid from entering the nozzle 46 after the gate valve 44 is installed. The upper seal may be ring-shaped or it may embody the shape of the lower end of the nozzle 46, which has been cut to fit on the hole cut on top of the cylindrical pipe 32. Either way, the upper seal is prone to failure as it is exposed to substantial wear and tear as the cartridge and paddle 180 pass through the lower end of the nozzle 46 and through the hole cut into the pipe 32 as the gate valve 44 is opened and closed.
Another problem associated with such gate valves is the proper alignment of the gate valve 44 in the nozzle 46. Specifically, the paddle 180 must be lined up perpendicular to the axis of the pipe 32 or the flow through the pipe 32. To accomplish this, a pair of keys (not shown) is provided on the cartridge, which must be lined up with slots (not shown) that are manually cut in the inner surface of the nozzle 46. Over time, the keys may corrode and tend to stick in the slots, which may also be subject to corrosion. Not only does this system not work very well for larger, heavier valves, it requires a time consuming and costly manufacturing process.
Accordingly, improved gate valve assemblies that may be installed in pressurized pipes and conduits are needed.